In the manufacturing process of liquid crystal display devices, organic light emitting diode (OLED) display devices and the like, substrates are often transferred among different processing equipments. As the substrates are very thin and thus may be damaged easily, they can not be carried directly. Instead, the substrates are placed into a special “substrate cassette” for transportation.
As shown in FIG. 1, a substrate cassette 1 includes a multi-layered framework, on each layer of which, one substrate 9 is placed, and mullions 11 are longitudinally arranged on both sides of the framework. Normally, there should be a gap of several millimeters between each of the both sides of the substrate 9 and each of the mullions 11 respectively. However, duo to the displacement of equipment or other reasons, the relative positions of the substrate 9 and the substrate cassette 1 may not be correct. As a result, the substrate 9 is likely to collide with an inner side (i.e., a side facing a space for housing the substrate 9) of each of the millions 11. As the substrate cassette 1 is usually made of metal and thus has a high hardness, the substrate 9 is easily damaged when it collides with the mullions 11.